Generally, a mobile communication system has been developed to provide a voice service while securing activity of a user. However, the mobile communication system gradually extends an area from a voice service to a data service. At present, the mobile communication system has been developed to provide a high-speed data service. However, since the current mobile communication system that is providing services suffers from a resource shortage phenomenon and does not meet a user demand for higher-speed services, there is a need for a more developed mobile communication system.
Meanwhile, if a device performs direct communication with an opponent device without using a base station, the device uses relatively less radio resources when performing communication using the existing radio network than when performing communication using the base station, and therefore has a great advantage in radio resource efficiency.
Further, since a method for discovering devices around a device is supported, a device may directly provide required information to devices that want the information, thereby greatly increasing efficiency in supporting an advertising service, a social networking service (hereinafter, SNS), or the like.
By the way, when device to device communication is performed, a device is connected to both an opponent device and a base station and when a device is linked to discontinuous reception, a receiver needs to be periodically operated to confirm whether there are transmission data from the opponent device, such that current consumption is highly likely to be increased.